Study of Synergistic Effect of Ce- and S-Codoping on the Enhancement of Visible-Light Photocatalytic Activity of TiO2

Different samples of Ce- and S-codoped TiO2 nanoparticles were prepared through simple sol-gel synthesis method by using cerium nitrate hexahydrate as cerium precursor, thiourea as sulfur, and tetrabutyl titanate (TBOT) as titanium precursor. Characterization of prepared samples were done by various techniques such as, X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. The XRD showed the presence of only anatase TiO2 for the single sulfur-doped and cerium- and sulfur-codoped titania samples. XRD analysis also pointed out the decrease in the crystal size with the increase in Ce concentration in the samples. The BET analysis reported an increase in the surface area and decrease in the pore size with the increase in the Ce concentration. The PLS results of the samples first showed a decrease in the intensity of the spectra sync with the reduction of recombination centers when the Ce was introduced in codoped TiO2 with the maximum decrease for 0.04 Ce/S-codoped titania; with the further increase in the Ce concentration in the samples, the intensity of the spectra gradually increased coinciding with the increase in the recombination centers. The recombination centers exhibit a direct relationship with the photocatalytic activity of the samples, which could be evidenced by the decolorization of 25 mg/L solution of AO-7. The activity of codoped samples was first increased by the incorporation of Ce with the maximum degradation for 0.04 cerium- and sulfur-codoped titania. By the further increase in the Ce amount in the Ce- and S-codoped titania samples the activity was shown to decrease gradually.